Sherlock will soon get a blast from the past: John Hannah has been cast as Sherlock's old drug dealer from London, executive producer Rob Doherty announced Saturday at Elementary's winter TV preview panel.

CBS boss teases HIMYM, Men futures, talks Jennifer Esposito

TVGuide.com has since learned that Hannah will play Rhys, who comes to New York seeking Holmes' (Jonny Lee Miller) help. "Rhys is somebody who was helpful to Sherlock in London every once in a while with respect to cases," Doherty tells us. "Rhys was a guy who had his finger on the pulse of crime in London. That's all in the past.

"When we meet him in the present, he has sought Sherlock out because several years ago he saw an opportunity to retire from the business: He ripped off his bosses and made off with about $2 million and retired to Thailand. His daughter, who actually lives in New York, has been abducted and is being held for ransom. He comes to Sherlock because even Rhys understands and appreciates that on drugs or off drugs, Sherlock Holmes is the greatest detective in the history of detecting."

Elementary Scoop: When will we meet Irene Adler?

Naturally, having his former dealer in town will not be easy for the recovering addict Sherlock. "It's difficult for Sherlock to be around him in that Rhys is a walking, talking trigger," Doherty says. "It's hard to interact with him and not remember his druggie past. So, Joan [Lucy Liu] has to work a little harder than usual."

For her part, Joan will not be a fan of Rhys. "Rhys is a lovely fellow, as is John Hannah, but her guard is up," he says. "She recognizes that as lovely as he may be, he's a criminal. He was a drug dealer. There are reasons to be a little wary of the guy. She's especially uncomfortable that Rhys is staying at the Brownstone."

Elementary airs Thursdays at 10/9c on CBS.

View original Elementary Scoop: John Hannah Cast as Sherlock's Former Drug Dealer at TVGuide.com